Polyalpha-olefins (PAOs) comprise a class of hydrocarbons typically manufactured by the catalytic oligomerization (polymerization to low-molecular-weight products) of linear alpha-olefin (LAO) monomers. These typically range from 1-octene to 1-dodecene, with 1-decene being a suitable material, although oligomeric copolymers of lower olefins such as ethylene and propylene may also be used, including copolymers of ethylene with higher olefins. PAO products have achieved importance in the lubricating oil market. Typically there are two classes of synthetic hydrocarbon fluids (SHF) produced from linear alpha-olefins, the two classes of SHF being denoted as PAO and HVI-PAO (high viscosity index PAOs). PAOs and HVI-PAOs of different viscosity grades are typically produced using promoted BF3 or AlCl3 catalysts. Subsequent to polymerization, the PAO lubricant range products are typically hydrogenated in order to reduce the residual unsaturation, generally to a level of greater than 90%.
Synthetic PAOs have found wide acceptability and commercial success in the lubricant field for their superiority to mineral based lubricants. In terms of lubricant property improvement, industrial research efforts on synthetic lubricants have led to PAO fluids exhibiting useful viscosities over a wide range of temperature, i.e., improved viscosity index, while also showing lubricity, thermal and oxidative stability and pour point equal to or better than mineral oil. These relatively new synthetic lubricants lower mechanical friction, enhancing mechanical efficiency over the full spectrum of mechanical loads and do so over a wider range of operating conditions than mineral oil lubricants.
Efforts have been made to prepare various PAOs using metallocene catalyst systems where PAOs are produced from meso-forms of certain metallocene catalysts under high hydrogen pressure. The use of rac-ethyl-bis(indenyl) zirconium dichloride or rac-dimethylsilyl-bis(2-methyl-indenyl) zirconium dichloride in combination with MAO at 40° C. (at 200 psi hydrogen or 1 mole of hydrogen) to produce isotactic polydecene have also been reported. Others have made various PAOs, such as polydecene, using various metallocene catalysts not typically known to produce polymers or oligomers with any specific tacticity.
To date however, PAOs made with metallocenes have not found wide applicability in the marketplace, particularly the lubricant marketplace, due to inefficient process, cost and property deficits. Accordingly, there exists a need in the art for providing PAOs and or HVI-PAOs and an improved process to produce them. There is a need in the art for new and improved catalysts and catalyst systems to obtain new and improved PAOs, polymerization processes, and the like. Accordingly, there is a need in the art for new and improved catalyst systems for the polymerization of olefins, in order to achieve specific properties.